One-dimensional arrays and strings:

Chapter 6, Slide 1

itemwith

index 0

itemwith

index 1

itemwith

index 2

itemwith

index 3

The concept of array - an extension of the basic model of memory:

Chapter 6, Slide 2

Accessing one-dimensional array via a pointer:

itemwith

index 0*p

itemwith

index 1*(p+1)

itemwith

index 2*(p+2)

itemwith

index 3*(p+3)

p

Chapter 6, Slide 3

constint* x x[0]

*(x+0)x[1]

*(x+1)x[2]

*(x+2)x[3]

*(x+3)x[4]

*(x+4)x[5]

*(x+5)

Representation of the int x[6] array:

• The size of the array is “forgotten” (after passing it to a function), no index range run-time testing is possible.

• Arrays passed by reference, as the pointer representing it is passed by value.

Chapter 6, Slide 5

void doit(int y[]){ y[0] = 0; y[1] = 1;}

int main(){ int i; int x[6]={10,11,12,13,14,15};

doit(x); for(i = 0; i < 6; i++) printf("%d ",x[i]); putchar('\n'); return 0;}

Chapter 6, Slide 6

80804048

int* x x[0]y[0]

0 1 12 13 14 15

x[1]y[1]

x[2] x[3] x[4] x[5]

address80804048

address80804052

address80804056

address80804060

address80804064

address80804070

doit() activation frame

80804048

int* y

The program displays: 0 1 12 13 14 15

Chapter 6, Slide 7

Dynamic one-dimensional arrays is simple:

int main(){ int i; int* x; x = malloc(6*sizeof(int)); if (x == NULL) exit(1);

x[0] = 10; x[1] = 11; x[2] = 12; x[3] = 13; x[4] = 14; x[5] = 15;

Chapter 6, Slide 7

for(i = 0; i < 6; i++) printf("%d ",x[i]); putchar('\n');

return 0;}

Strings are char arrays terminated by NULL '\0'

Thus a string can be stored in a static array:

char x[30] = "hello";or char x[30]; strcpy(x,"hello");

Chapter 6, Slide 8

as well as in a dynamic array

char* x;x = malloc(30);strcpy(x,"hello");

Thus a string is represented by a pointer and passed by reference.

char* strcpy(char* dest,const char* src){ char *dest1 = dest; while((*dest++=*src++) != NULL); return dest1;}

Chapter 6, Slide 9

Missing NULL could spell big troubles (see overflows).

Not allocating memory for a string is the most common error (leading to erratic behaviour):

int main(){ char* p; strcpy(p,"hello"); return 0;}

Insufficient memory could spell troubles (overflows):

p = malloc(5); strcpy(p,"hello");

Chapter 6, Slide 10

In C++ we can overload operator [] and create “arrays” with range checking: chapter6_1

End of slides for chapter 6